Secretary of State John Kerry gestures during a news conference at the NATO headquarters in Brussels April 23. Kerry said on Tuesday that NATO needed to consider its role in the Syrian crisis, including how practically prepared it was to respond to a potential chemical weapons threat.

Beyond that point, however, former officials and analysts are split over why Mr. Obama is so cautious about the issue – he even refused to answer a reporter’s question on the topic Tuesday – and what the apparently high bar the administration has set for evidence of chemical weapons use means.

“It’s a hard call as to whether the administration is trying to avoid something, or if they just don’t have the evidence,” says Wayne White, a former State Department official with experience in Middle East intelligence.

Obama has said repeatedly since last August that Syria’s use of chemical weapons is a US “red line” and would be a “game changer” for the US. But now some critics say the president’s caution suggests a moving or “fuzzy” red line.

For some, the president is simply being prudent, especially if the evidence presented so far is “inconclusive,” as a number of senior administration officials, including Defense Secretary Chuck Hagel, have said. Obama, they add, wants to avoid a rush to judgment that turns out to be mistaken – and which could appear to the world like a repeat of the 2003 US decision to invade Iraq over weapons of mass destruction that didn’t exist.

White House spokesman Jay Carney said Tuesday that the US is being “extremely deliberate” in investigating and evaluating the reports of chemical weapons use. And on Wednesday in Cairo, Secretary Hagel suggested the US would not be rushed to judgment by allies, saying, “Suspicions are one thing. Evidence is another.” He then added, “I think we have to be very careful here before we make any conclusions.”

But for others, the reason Obama is setting the bar high – in a situation where incontrovertible evidence could remain very difficult to come by – is because he has no desire to ratchet up US involvement in the Syrian conflict unless forced to.

The danger of this approach, critics say, is that it encourages an increasingly desperate President Assad to test the limits of US reluctance – perhaps even with limited, hard-to-prove use of some chemical weapons.

And even if some isolated use of chemical weapons is proved, some analysts say, Obama is still unlikely to intervene in Syria in a manner that could tip the scales in the conflict.

“Even if CW [chemical weapons] were used, [the response] will depend a bit on how much and what we’re talking about,” says Mr. White, the former State Department official.

If chemical weapons use is proven “there will have to be some response from the administration,” he adds, “but unless it’s indiscriminate use, I don’t see us doing something like a no-fly zone that could really make a difference.”

Given Obama’s pattern to this point of gradually ramping up humanitarian aid and non-lethal material assistance to the rebels, the administration might bow to French and British pressure to approve providing the rebels with arms, White says. “But something like that, that might have made a difference 18 months ago, won’t be a game-changer now.”

That’s because the rebels are now so divided, and because the groups the US would be willing to arm are not the ones – specifically the more extremist Islamist factions – achieving advances against Assad on the battlefield.

White, who is now an adjunct scholar at the Middle East Institute in Washington, says the administration may be “playing for time,” with its talk of deliberate evaluation of evidence, as it tries to overcome its deep divisions over how the US should approach the complex and ever-deepening Syria crisis.

But it also may be that the “evidence” its allies have provided the US – supposedly photos of victims with tell-tale signs of chemical-weapons contact from the Israelis, soil samples in the case of the French and British – isn’t very convincing.

British military intelligence officials originally reported in late March their finding that Assad’s forces had actually used an intense military-grade tear gas in a reported attack March 19 on the city of Halab. Reports claimed that 30 people died in the attack, but the tear gas is not a chemical weapon and it was not clear what caused the deaths.

White says Iraq’s Saddam Hussein – who used chemical weapons to kills thousands of Kurds in 1988 – also used a military grade tear gas known as CS on Iranian troops who were advancing on the southern Iraqi city of Basra in 1982. The gas repelled the Iranian forces but did not kill them by the thousands as a nerve gas would have, White says.

The United Nations has formed an investigative group to go into Syria and determine what chemical weapons if any were used, but so far Assad is not letting the team in. And without such a team on the ground, it may remain impossible to deliver the kind of “conclusive evidence” the Obama administration says it has yet to see.